1. Field of the Invention
The present invention relates generally to implantable defibrillation leads and electrodes, and more particularly to methods for the sub-xiphoid implantation of deployable defibrillation electrodes, and means for anchoring the same to tissue within the pericardium.
The pericardium is a membranous sac that encloses the heart. It consists of an outer layer of dense fibrous tissue and an inner serous layer, termed the epicardium, which directly surrounds the heart. Throughout the description and claims that follow, the phrase "within the pericardium" or "within the pericardial space" is used to mean any of the body tissue or fluid found inside of the dense outer layer of the pericardium, including the outer surface of the heart, but not including the interior of the heart.
In recent years a serious effort has been undertaken to implant automatic defibrillators in certain patients at high risk of experiencing ventricular fibrillation or other heart disorders. When fibrillation or related heart malfunctions are sensed by such devices, a large defibrillation shock is automatically delivered to the heart in an attempt to stimulate the heart back to a normal or near normal beating pattern. The advantage of such implanted devices is that the life-saving defibrillation shocks are delivered without any undue delay, as would otherwise exist if external defibrillation pulses had to be delivered by paramedics (or other medical personnel) who were summoned to the aid of a heart-failing patient.
In order to minimize the energy of a defibrillation pulse, and thereby improve the efficacy of the defibrillation system, it is preferred that the defibrillation electrodes be in direct contact with the heart tissue. Further, it is generally preferred that the electrodes cover large and strategic areas of the heart, thereby allowing the delivered electrical energy to be efficiently distributed throughout the fibrillating region. Attempts at placing the defibrillating electrodes on the inside of the heart, either in the atria or the ventricles, or both, similar to stimulating electrodes used with pacemakers, have proven less than satisfactory.
Accordingly, implantable defibrillation electrodes are preferably placed around the exterior of the heart. Because of the large surface area covered by such electrodes, they are typically referred to as "patch electrodes", often resembling patches that are placed on the heart. Although there are some shortcomings associated with placement of defibrillation electrodes directly on the epicardial or endocardial surfaces, the advantages are overwhelming.
In order to make the best possible contact with the heart tissue, it is often desirable that implantable defibrillation electrodes be placed within the pericardium, or within the pericardial space. Unfortunately, however, pericardial placement of defibrillation leads is a dangerous and difficult procedure that has heretofore generally required traumatic and endangering surgery, usually open-chest surgery. Needless to say, not all patients are suitable candidates for open-chest surgery, and even for those that are, the risks, trauma, and danger associated with such surgery make this procedure of electrode placement less than ideal.
In an attempt to minimize the problems associated with open-chest surgery for the placement of epicardial defibrillation leads, it has been suggested in the art to implant epicardial defibrillation leads transvenously. Such an approach is described in patent application Ser. No. 07/128,326, filed Dec. 3, 1987, entitled "Method For Transvenous Implantation of Objects into the Pericardial Space of Patients," jointly invented by the applicant named herein and Clyde D. Elliott. This prior application, including the methods and leads described therein (hereafter referred to as the "transvenous implantation approach"), is hereby incorporated herein by reference.
In accordance with the transvenous implantation approach described in the above-referenced prior application, a guide wire and a catheter are inserted into the heart transvenously, with the aid of an introducer, as required. Once in the heart, the atrial lateral wall is punctured, making a hole therein, through which the non-deployed defibrillation electrode is inserted, thereby entering the pericardial space. The non-deployed electrode is further positioned within the pericardial space to a desired position, and then the electrode is deployed so as to better contact a larger surface area of the outside of the heart.
The transvenous implantation approach also suffers from several drawbacks. For one, a fairly good size hole must be made in the atrial wall, and the trauma and long term effects of such a hole are uncertain. Further, the approach is generally limited to an introducer not much larger than a Fr 14. (A FR 14 instrument is approximately 4.7 millimeters in diameter.) Additionally, the introducer's path is somewhat tortuous, resulting in challenging lead placement. Moreover, once the lead is placed, the ensuing connection of the lead to the site of the implanted defibrillator is non-trivial.
From the venous location of the lead, the lead connector must then be tunneled to the defibrillator site, generally in the abdomen. These limitations place severe restrictions on the geometry and flexibility of the electrode and the deployment system. For small, easily deployed lead systems, the transvenous implantation approach offers a very viable alternative to open chest surgery, particularly if a long tunneled lead is not objectionable. However, in the event very large surface electrodes are desired, or if tunneling is undesirable, the transvenous approach is probably no more effective, and perhaps less effective, than a more direct surgical approach. What is needed, therefore, is a method and system for placing defibrillation leads in the propitious pericardial space that avoids the major problems associated with both the open-chest surgery approach and the transvenous implantation approach. The present invention advantageously addresses this need.